/**
 \defgroup buildsystem The Contiki build system

 .
 
 The Contiki build system is designed to make it easy to compile
 Contiki applications for either to a hardware platform or into a
 simulation platform by simply supplying different parameters to the
 <tt>make</tt> command, without having to edit makefiles or modify
 the application code.

 The file example project in examples/hello-world/ shows how the
 Contiki build system works. The <tt>hello-world.c</tt> application
 can be built into a complete Contiki system by running <tt>make</tt>
 in the examples/hello-world/ directory. Running <tt>make</tt> without
 parameters will build a Contiki system using the <tt>native</tt>
 target. The <tt>native</tt> target is a special Contiki platform that
 builds an entire Contiki system as a program that runs on the
 development system. After compiling the application for the
 <tt>native</tt> target it is possible to run the Contiki system with
 the application by running the file <tt>hello-world.native</tt>. To
 compile the application and a Contiki system for the \ref esb "ESB
 platform" the command <tt>make TARGET=esb</tt> is used. This produces
 a hello-world.esb file that can be loaded into an ESB board.

 To compile the hello-world application into a stand-alone executable
 that can be loaded into a running Contiki system, the command
 <tt>make hello-world.ce</tt> is used. To build an executable file for
 the ESB platform, <tt>make TARGET=esb hello-world.ce</tt> is run.

 To avoid having to type <tt>TARGET=</tt> every time <tt>make</tt> is
 run, it is possible to run <tt>make TARGET=esb savetarget</tt> to
 save the selected target as the default target platform for
 subsequent invocations of <tt>make</tt>. A file called
 <tt>Makefile.target</tt> containing the currently saved target is
 saved in the project's directory.

 \section buildsystem-makefiles Makefiles used in the Contiki build system
 
 The Contiki build system is composed of a number of Makefiles. These
 are:
 - <tt>Makefile</tt>: the project's makefile, located in the project directory.
 - <tt>Makefile.include</tt>: the system-wide Contiki makefile,
 located in the root of the Contiki source tree.
 - <tt>Makefile.\$(TARGET)</tt> (where \$(TARGET) is the name of the
 platform that is currently being built): rules for the specific
 platform, located in the platform's subdirectory in the platform/ directory.
 - <tt>Makefile.\$(CPU)</tt> (where \$(CPU) is the name of the CPU or
 microcontroller architecture used on the platform for which Contiki
 is built): rules for the CPU architecture, located in the CPU
 architecture's subdirectory in the cpu/ directory.
 - <tt>Makefile.\$(APP)</tt> (where \$(APP) is the name of an
 application in the apps/ directory): rules for applications in the
 apps/ directories. Each application has its own makefile.

 The Makefile in the project's directory is intentionally simple. It
 specifies where the Contiki source code resides in the system and
 includes the system-wide Makefile, <tt>Makefile.include</tt>. The
 project's makefile can also define in the <tt>APPS</tt> variable a
 list of applications from the apps/ directory that should be included
 in the Contiki system. The Makefile used in the hello-world example
 project looks like this:

 \code
CONTIKI = ../..
all: hello-world
include $(CONTIKI)/Makefile.include
 \endcode
 
 First, the location of the Contiki source code tree is given by
 defining the <tt>CONTIKI</tt> variable. Next, the name of the
 application is defined. Finally, the system-wide
 <tt>Makefile.include</tt> is included. 

 The <tt>Makefile.include</tt> contains definitions of the C files of
 the core Contiki system. <tt>Makefile.include</tt> always reside in
 the root of the Contiki source tree. When <tt>make</tt> is run,
 <tt>Makefile.include</tt> includes the <tt>Makefile.\$(TARGET)</tt>
 as well as all makefiles for the applications in the <tt>APPS</tt>
 list (which is specified by the project's <tt>Makefile</tt>).

 <tt>Makefile.\$(TARGET)</tt>, which is located in the
 platform/\$(TARGET)/ directory, contains the list of C files that the
 platform adds to the Contiki system. This list is defined by the
 <tt>CONTIKI_TARGET_SOURCEFILES</tt> variable. The
 <tt>Makefile.\$(TARGET)</tt> also includes the
 <tt>Makefile.\$(CPU)</tt> from the cpu/\$(CPU)/ directory.

 The <tt>Makefile.\$(CPU)</tt> typically contains definitions for the
 C compiler used for the particular CPU. If multiple C compilers are
 used, the <tt>Makefile.\$(CPU)</tt> can either contain a conditional
 expression that allows different C compilers to be defined, or it can
 be completely overridden by the platform specific makefile
 <tt>Makefile.\$(TARGET)</tt>. 
@{
 */

 /**
 @}
 */
 
